Hotel staff found several youths lying motionless on the pool’s deck after CO levels reached 16 times the safe limit.

A 13-year-old boy was killed and 12 people were hospitalized when a visit to a hotel’s indoor swimming pool led to carbon monoxide poisoning, authorities said.

Several children had been swimming at the Quality Inn in Niles, Michigan, around 10 a.m. Saturday when a passing member of the hotel’s staff peered through a window and saw them lying unconscious on the deck, local fire officials said.

Six children between 12 and 14 years of age were rushed to local hospitals. One boy, since identified as Bryan Douglas Watts, died en route, local station WNDU reported.

Hotel staff members and police officers who responded to the emergency were also taken to area hospitals after being exposed to the toxic air.

According to WNDU, the CO levels were later determined to be 16 times the safe limit.

A carbon monoxide leak at a Michigan hotel’s swimming pool left one child dead and 12 people hospitalized.

Niles Fire Department Capt. Don Wise said he suspects the pool’s heater is to blame.

“Anything that has a natural gas heater has a potential of putting off carbon monoxide,” Wise told reporters at the scene. “Carbon monoxide is colorless, odorless and tasteless. You’ll end up getting flu-like symptoms… Patients will get nauseous, maybe vomit.”

Wise added that it was pure chance the children were found when they were. He credited the hotel’s staff with opening the doors, which allowed fresh air to get in.

“Staff just happened to walk by the window and [see] the kids unresponsive on the deck, and then they reacted,” he said. “But no one really knows when the last time somebody saw them actively moving around [was].”

One hotel guest described hearing the children playing before laughter turned to screams.

“At first I thought someone drowned, because when I came out of my room, there was a body lying on the floor in the hallway and then there was five of them lying by the pool,” the woman, who was not identified, told Reuters.

As authorities worked to remove and resuscitate the children, the hotel was evacuated as a precaution. Wise said the pool area did not have a carbon monoxide detector.